1. Field of the Invention
This invention relates to arranging randomly-listed sets of test points in a preferred sequence, and more particularly, to arranging sets of test points in a sequence minimizing the time required for test probes to travel among the sets of test points in the order of the sequence.
2. Background Information
The electronics industry has developed a number of products manufactured by processes including electrical testing to ensure product quality. In such products, a typical circuit board, or substrate, includes a number of conductive points or nodes exposed at one side of the board to a test process. In a properly made circuit board, certain of the test points are connected by electrical circuits, while other pairs of test points, forming parts of separate circuits, are not electrically connected.
A first part of the testing process involves checking for "opens," or open circuit conditions between various pairs of test points which are supposed to be electrically connected. For this testing, a pair of test probes is brought into simultaneous contact with the two test points, allowing a test circuit to determine electrical continuity. A second part of the testing process may involve checking for "shorts," or unwanted electrical connections between separate circuits. This type of testing can be performed using a two-probe method, in which a pair of test probes is brought into simultaneous contact with a test point on each of a pair of circuits which should not be electrically connected. If electrical continuity is detected, a short extends between the circuits.
The detection of short circuits can also be accomplished using a single probe, together with a conductive plane. The single probe is sequentially moved into contact with a number of test points on one side of the card. Each test point is electrically connected to a circuit, and the capacitance between the circuit and the ground plane is measured in the testing process. If a multi-level circuit board is being tested, a ground or voltage plane within the circuit board may be used to establish the conductive plane; otherwise the side of the board opposite the test points is laid on a flat conductive surface. The presence of a short circuit connecting two or more circuits is detected through an increase in the capacitance between these circuits and the conductive plane.
The circuit testing devices described in the co-pending applications cross-referenced above are examples of devices, performing this type of testing, which can benefit greatly from a method to order the sequence in which sets of test points are accessed to minimize the time needed to drive the probes between such sets of test points.